Recently, a hybrid working machine has been practically used in which an engine and a generator motor mechanically coupled to the engine are provided as a driving source and an electric actuator is rotationally driven by the electric energy generated by the generator motor. In such a hybrid working machine, the electric energy stored in a battery to be described later or the electric energy generated by the generator motor is used when accelerating (performing a power running action of) the electric actuator, and a power generation action of the electric actuator is performed and the generated electric energy is stored in the battery when decelerating (performing a regeneration action of) the electric actuator. As the battery, a nickel hydride battery as a so-called secondary battery, a lithium ion battery, a capacitor, or the like is used. For example, the capacitor may charge and discharge the electric energy in a short time, and has a characteristic in which a large amount of electric energy (charge) may be charged and discharged. Thus, the capacitor is mounted on the hybrid construction machine.
When performing maintenance such as a replacement of the capacitor or the capacitor peripheral unit or an inspection of a deterioration state of the capacitor, there is a need to perform charge extracting (discharging) of the capacitor. When discharging not only the capacitor but also the secondary battery, the capacitor may be taken out from the hybrid working machine and the charge extracting may be performed by using a tool such as a discharger. However, when the process of extracting the charge of the capacitor mounted on the hybrid working machine may be performed by a structure in which the electric energy is consumed (discharged) by using the engine as a load while the capacitor is provided inside the hybrid working machine or a control device (a charge/discharge device) is provided in the hybrid working machine and the charge extracting is performed by using the charge/discharge device, there is no need to perform a troublesome work in which the discharger is carried to the site where the hybrid working machine is operated. That is, the hybrid working machine is provided with the charge/discharge device and power is supplied (discharged) from the capacitor to the generator motor rotationally driven with the driving of the engine so as to drive the generator motor by using the operating engine as a load, thereby performing the discharging (the charge extracting) of the charge in the capacitor.
Furthermore, Patent Literature 1 discloses a configuration in which an engine as a load is driven and a current and a voltage of a generator motor and a booster are controlled so as to promptly extract a charge of a capacitor. Further, Patent Literature 2 discloses a configuration in which any one of discharging control of driving an engine starting motor by a running battery using an engine as a load and charging control of rotationally driving the engine starting motor by the engine to charge the running battery is performed and the IV characteristics of the battery are calculated based on the battery current and voltage at that time so as to inspect the battery deterioration state.